This invention relates to an improvement of a system for disposing radioactive gaseous wastes in a nuclear power plant.
In a nuclear power plant, such as a lightwater type nuclear reactor, a portion of coolant, i.e. water, is decomposed into oxygen and hydrogen by the irradiation of neutrons during a time when the coolant passes through a reactor core. Simultaneously, radioactive isotopes such as .sup.3 H, .sup.16 N and .sup.19 O are generated and argon in a small amount of air contained in the cooling water also changes to radioactive isotopes of .sup.37 Ar and .sup.41 Ar. These radioactive isotopes and mixed with steam and fed into a steam turbine system of the nuclear power plant. Therefore, it is necessary to maintain the safeness of the surroundings of the steam turbine system by providing a shielding equipment.
However, since the radioactive gaseous wastes discharged into the main condenser of the turbine system are generally non-condensable, they will stay at the upper portion thereof. The gaseous wastes staying at the upper portion of the main condenser are extracted to the outside of the turbine system by an air extractor and the extracted gaseous wastes are heated by steam generated by a boiler located in the power plant so as to recombine oxygen and hydrogen contained in the gaseous wastes in a recombiner. The recombined water vapour and the gaseous wastes are then fed into a condenser located downstream of the recombiner and cooled there by cooling water. The cooled vapour is liquefied into condensed water, separated from the gaseous wastes and returned to the main condenser. After separation of the vapour the gaseous wastes are sent to an adsorbing device utilizing an activated carbon through an attenuating pipe and a dryer in which radioactive wastes having short lifetime and moisture are fully removed. The remaining radioactive gaseous wastes mainly consisting of isotopes of Xe and Kr are adsorbed and held up for a long time by the activated carbon in the hold-up device. Thus, the gaseous wastes containing gases having radioactivity considerably lesser than a permissible radioactivity are discharged into atmosphere from a discharging stack.
In a conventional system, described above, for disposing radioactive gaseous wastes, it is necessary to provide pipes for connecting equipment such as a preheater, recombiner and a condenser which are independently located in the disposing system. These pipes are likely subjected to a stress caused by heat or earthquakes during the operation of the nuclear power plant and the stress acts on nozzles of the equipment as a reactive force. This stress or reactive force is undesirable for the equipment in the nuclear power plant.
In order to reduce the heat stress applied to the pipes, the pipes have been bent many times as far as possible to have sufficient flexibility, but this arrangement requires a number of pipe supporting members and a large space for installing the pipes and members. In addition, the use of long pipes for connecting the equipment of the power plant requires much work including the welding of the pipes in a field and the existence of the welded portions decreases the reliability of the equipment. Moreover, since a plurality of pipes are used, the temperature of the gaseous wastes once preheated by a preheater is lowered by the heat loss from the surfaces of the pipes, thereby decreasing the recombining effect between the oxygen and the hydrogen in the gaseous wastes. All defects described hereinabove are based on the fact that the various equipment in a radioactive gaseous waste disposing system are independently arranged and connected by a plurality of pipes.